A number of aromatic and cyclic phosphorus containing stabilizers for polymers are known. Some of these are effective against heat degradation of polymers and some of them find use in combination with other stabilizers for the same or different functions, protection against ultra-violet light degradation for example. Many of these cyclic phosphorus containing materials are expensive and they have varying degrees of effectiveness when combined with other stabilizers. Further, some of the most effective materials have some deficiencies such as lack of hydrolytic stability and the like. New cyclic phosphites that are effective anti-oxidants, are readily and inexpensively prepared, and that particularly exhibit enhanced polymer protection when combined with hydroxyphenylalkylenyl isocyanurate compounds are desired.